TRUCK IS ACTING CRAZY

[JACK34]

Temp sensor: Yes a bad or unhooked temp sensor (to the PCM) can spooof a truck into thinking it'a temperature outside ..that it's not. So the air/fuel will be wrong. Glad you're fixing that.

Grounds: You can't have too many grounds. All electricity travels from the grount TO the positive (not the other way around). It's electron movement from negative to positive. Thats why grounds ...good grounds are so important. Bad grounds mean poor electrical movement. Computer chips don't like 'partial' or 'flaky' power. They act flaky when power is not good and consistent. Newer vehicles have grounds all over the body coming from the wire harness. Braided cable (or any multi strand 'fine' cable) because electron movement is on the surface, not through the center of the cable. So a fine braided cable will perform best.

70s era trucks. Hey they look nice, fun to drive once in a while. But they drive like 70's era trucks. Creature comforts were no where near as good as newer vehicles. Remember those 70's trucks on a -20 morning? You could hardly start them and they were cold as can be inside. LOL. Carbs, chokes and vacuum problems were a problem too. I remember those days and those truck very well. One nice thing about early GMT trucks is they are still simple enough ...not TOO MANY computers (compared to new).

Hope now that you have yours fixed it's good for many trouble-free miles....

Cheers

Thank you for the information on the temp sensor and the info on the grounds. Ive done all I can for now if it's not grounded good now it probably never will be. I agree with you on the 70's era trucks. Thank you.

 

[PlayingWithTBI]

Mine is a 94 where is the one on the head located?

It's between #s 1&3 exhaust ports, it's a 1 wire sensor. There were 2 different ones for our trucks, a sensor and a sender. The sensor is for a gauge and the sender is for an idiot light, usually found in the base model W/Ts.

 

[JACK34]

It's between #s 1&3 exhaust ports, it's a 1 wire sensor. There were 2 different ones for our trucks, a sensor and a sender. The sensor is for a gauge and the sender is for an idiot light, usually found in the base model W/Ts.

Mine has both. Going to replace the one on the head tomorrow. Thank you.

 

[1998_K1500_Sub]

I'd go from the fuel pump boss to the battery.

Don’t do that… if you do, the frame won’t have a low resistance connection to the ALT / engine.

Don’t change the OE grounding plan.

Notice how the OE grounds form a star (excepting for the relatively light gauge wire to the passenger’s fender from the battery neg), rooted at the passenger’s side engine/ frame / firewall.

Folks, there’s a reason for that.

Don’t go ape$h1t and start adding grounds or re-arranging grounds without careful consideration.

 

[Jeepwalker]

Also, check your battery voltage and have it load-tested (any auto parts store can do it for free). A battery that's 'on the edge' can make a vehicle act funny. Maybe you already replaced it, I don't remember..

 

[Erik the Awful]

Does anyone have a resistance calculator to determine how much more resistance that added?

Right now? Nearly none. The problem is that in ten years there's going to be corrosion in that strap. It also looks goofy having a ground strap a mile long. I'd shoot a little PB Blaster on that strap to give it a fighting chance.

Don’t do that… if you do, the frame won’t have a low resistance connection to the ALT / engine.

So connect it to the frame then. The engine, body, frame, and battery should all be connected by ground straps.

 

[1998_K1500_Sub]

So connect it to the frame then. The engine, body, frame, and battery should all be connected by ground straps.

Battery should grounded to the engine, that’s a high-current path (ALT charging current to BAT).

The engine (and thus ALT and BAT) is then grounded to the frame at a single point.

I’m just describing how the OEM designed it. They had their reasons for that design. I happen to agree with their reasoning.

 

[Erik the Awful]

They had their reasons for that design.

It was cheap and easy. We've already determined that the factory 4 gauge starter wiring was barely adequate at the time it was produced, so I don't hold much of their decision making in high regard.

Honestly, I was answering without knowing the exact factory layout. My truck's original wiring was long-butchered before I got it. What matters is that you have all four grounded, and that the path from starter to battery be thick enough to carry the starter's amperage draw.

 

[1998_K1500_Sub]

It was cheap and easy.

(adding) And generally effective.

I haven’t had starter cable problems, but I don’t deny them.

The routing of the headlight power circuit to the dash and back to the headlights was inferior to their later use of relays in the engine bay for that circuit.

the path from starter to battery be thick enough to carry the starter's amperage draw.

Yup… heavy cable from BAT to engine for both positive (to starter) and neg (to block).

Large wire from ALT POS output directly to BAT (alternative: to starter stud). ALT NEG output path to BAT is via engine block and same heavy NEG connection that was required by starter.

One (1) solitary “star” GND connection for engine & frame & firewall (this is typically made either at the frame or at a firewall stud, sometimes at engine).

No multiple GND paths.

We can now talk about how the loads are / should be connected, if anyone’s feeling chatty But that’s off topic for this thread.

 

[JACK34]

Don’t do that… if you do, the frame won’t have a low resistance connection to the ALT / engine.

Don’t change the OE grounding plan.

Notice how the OE grounds form a star (excepting for the relatively light gauge wire to the passenger’s fender from the battery neg), rooted at the passenger’s side engine/ frame / firewall.

Folks, there’s a reason for that.

Don’t go ape$h1t and start adding grounds or re-arranging grounds without careful consideration.

I didn't do that I just refused to take the almost impossible one off on the back of the passengers side head. Instead I mounted the braid to the mechanical fuel pump cover and ran it back where it was on the firewall. And replaced the one from the firewall to the frame with braid as well. Yes the one from the pump to the firewall is 20 or so inches longer. I cleaned all the other engine bay grounds as well and the battery terminals. I replaced the other temp sensor on the head today and it runs great. I understand this is a forum and opinions vary. Thanks for the info.